Ubiquitor is a member of an anicent race of beings called the Absolutes. An omnipotent race from trillions of years before the existence of the known Marvel universe, they moved through dimensions creating and destroying universes. They grew tired if this plane of existence and traveled to higher planes. Ubiquitor remained and continued to destroy universes one after another.
She gathered a group of aliens from various planets/dimensions/universes that she destroyed to become her Emissaries and sent them to attack and eliminate the Galactic Guardians. They failed, so she and her emissaries confronted them on the planet Klaatu (the Guardians homebase).
She wanted Phoenix IX to merge with her so they would become a more powerful Absolute, but he refused and she battled him, almost destoying him until Woden assisted. They were able to seemingly destroy her with their combined power and she has not been seen since.